1. Field of the Invention
The invention relates to a method for coating a tool or tool part, in particular a cutting element such as an insert, in which a base structure is provided and one or more layers are applied thereto, at least one layer being formed of a metal carbonitride of one or more of the metals titanium, zirconium, hafnium, vanadium, niobium, tantalum and/or chromium and being deposited by a gas containing methane, nitrogen and one or more metal compounds.
Furthermore, the invention relates to a coating applied to an object with at least one metal carbonitride layer of one or more of the metals titanium, zirconium, hafnium, vanadium, niobium, tantalum and/or chromium, e.g., a titanium carbonitride layer.
Furthermore, the invention relates to a tool or tool part, in particular a cutting element such as an insert, comprising a base structure with one or more layers applied thereto, at least one layer being a metal carbonitride layer.
2. Discussion of Background Information
Abrasively highly stressed tools, e.g., cutting, stamping or forming tools, are usually coated in order to counteract wear of the tools during use. Multilayer coatings with an outermost workpiece-side working layer and several layers or plies lying underneath are also thereby often used. Although multilayer coatings are more complex to produce than single-layer coatings, with the same thickness the multilayer coatings are less brittle and connected with greater flexibility when it is a matter of designing a coating in the best possible manner with respect to anticipated stresses.
From the prior art, multilayer coatings are known for inserts of lathe tools, which coatings have a titanium nitride layer or aluminum oxide layer as the outermost layer on the workpiece side during use, which layer is deposited directly or indirectly on a metal carbonitride layer such as a titanium carbonitride layer. The aluminum oxide layer, for example, is chemically inert and heat-resistant and thus protects the layers lying underneath. The supporting titanium carbonitride layer is characterized by great hardness and is intended to contribute to a wear resistance of the coating or of the tool. Further layers, in particular layers that adhere well to the base structure, can be provided between the connecting layer of titanium carbonitride and the base structure of the insert of hard metal, thus rendering possible a strong adhesive connection of the coating.
It must be taken into account with multilayer coatings that a great hardness of individual layers alone is not yet sufficient for a long operational life or service life. Even an extremely hard layer can no longer be useful if it detaches from the base structure or a layer lying underneath, which can occur in particular with inserts, which are subjected not only to high mechanical stresses, but also to high temperatures and/or temperature changes.
Particularly high demands are made on connecting layers or intermediate layers of metal carbonitride (MeCxNy) in this context, since their very function is to give the coating wear resistance and to bear a protecting working layer for a long time.
In particular, layers of titanium carbonitride are particularly frequently used as connecting layers in multilayer coatings or layer systems. The reason for this is that with known titanium carbonitride layers, carbon can be replaced consistently by nitrogen (or vice versa), whereby the properties of these layers can also be variably adjusted via the composition. Finally, layers of this type have properties that lie or can be set between those of titanium carbide and titanium nitride.
A production of titanium carbonitride layers can be carried out by CVD methods (chemical vapor deposition), as was the practice for many years. With CVD, the layers are deposited from a gas mixture containing methane, nitrogen, titanium tetrachloride and hydrogen as carrier gas at substrate temperatures from 950 to 1100° C. The titanium carbonitride layers thus obtained are composed of globular grain and form a dense layer.
In connection with the deposition of this so-called high-temperature titanium carbonitride on hard metal substrates, an undesirable decarburization of the substrate is often observed, even when a connecting layer, e.g., an 0.5 μm thick layer of titanium nitride, is provided between the hard metal and the titanium carbonitride layer. In order to curb this decarburization, there has recently been a switch to using gases containing titanium tetrachloride and acetonitrile for the deposition of titanium carbonitride, whereby a deposition temperature can be reduced to lower temperatures of 750 to 900° C. Titanium carbonitride produced in this manner is known as medium-temperature titanium carbonitride and has a columnar structure of rod-shaped crystallites, the thickness of which is more than 750 Å or 75 nanometers.
As mentioned, known high-temperature or medium-temperature titanium carbonitride layers are used primarily as connecting layers, on which further layers are or will be deposited. However, it has been shown that an adhesive strength of titanium nitride layers or other types of working layers can be insufficient on conventional titanium carbonitride layers as on other metal carbonitride layers, too, so that an operational life of the tool can be limited by a detaching of a working layer that is wear resistant per se.
In addition, known titanium carbonitride layers, and metal carbonitride layers in general, are also used as outermost layer arranged on the workpiece side, thus as a working layer. However, in practice they can thereby be used only in a very restricted manner: with layers of this type, when used as a working layer, despite great hardness, sticking and thus, a comparatively short service life, is to be anticipated.